A constant on-time controller can be used in a buck regulator device, the constant on-time controller can use a regulator output voltage ripple to initiate an on-time whenever a regulator output voltage falls below a reference voltage. An on-time is terminated (generating an on-time pulse) by circuitry in response to other conditions (such as a level of a regulator input voltage). During the on-time pulse, energy is supplied directly from the regulator input voltage to the regulator output voltage via an electronic switching device. Likewise, when the on-time pulse has terminated, stored energy in the energy storage inductor is supplied to the regulator output voltage.
The buck regulator device with the constant on-time controller usually include circuits that adjust the on-time pulse duration as a function of the regulator input voltage and regulator output voltage, thus resulting in an almost constant frequency as the duty cycle changes. The regulator output voltage ripple is determined to a large extent by a ripple current in the energy storage inductor flowing through an output capacitor's equivalent series resistance (ESR). In applications that the multilayer ceramic capacitor (MLCC) has the small ESR, such that the voltage ripple from the energy storage inductor is also small. This creates two problems for the constant on-time controller, stability and susceptibility to noise.